1. Field of the Invention
This invention relates to a foamable silicone rubber composition, and more particularly to a foamable silicone rubber composition from which a silicone sponge rubber having a great tensile strength can be obtained even when it has a low foam density.
2. Description of the Prior Art
As known in the art, silicone sponge rubber is usually obtained by curing and foaming a foamable composition mainly composed of an organopolysiloxane, and an inorganic filler or organic filler is added in order to improve the tensile strength of the silicone sponge rubber.
For example, the inorganic filler may include silica fillers surface-treated with organosilicon compounds such as organochlorosilane, organopolysiloxane and hexaorganosilazane (Japanese Patent Publication (kokai) No. 3-56542 corresponding to U.S. Pat. No. 4,987,115). The organic filler may include resin copolymers (Japanese Patent Publication (kokoku) No. 5-53823 corresponding to U.S. Pat. No. 4,418,157).
Addition of such fillers, however, can not bring about so much improvement in tensile strength of the resulting silicone sponge rubbers. The addition of inorganic filler may cause an increase in viscosity of compositions and a decrease in elasticity of silicone sponge rubbers (foams). It also results in an increase in production cost.